With the U.S. Senate set to vote Wednesday on ratification of the United Nation's Convention on the Rights of Persons with Disabilities (CRPD), some critics, including former U.S. Sen. Rick Santorum and homeschool advocates, warn the treaty could undermine parental rights.

Nations that ratify the CRPD agree to forbid discrimination against persons with disabilities, much like the United States has done with passage of the Americans with Disabilities Act of 1990. The CRPD was first negotiated during the George W. Bush administration and has been ratified by 126 nations.

While the treaty sounds beneficial, Santorum said Monday on CNN's "Piers Morgan Tonight," it would be harmful because it says the state, not parents, have authority over what is in the best interest of the child.

"This would be something unprecedented in American law, to give the state the ultimate authority as to what is the best interest of your child. Historically, the United States has been very clear, parents, unless they are unfit for some reason, get that decision," Santorum said.

Santorum is the father of a disabled daughter. Three-year-old Bella Santorum was born with trisomy 18, a rare genetic disorder. Santorum said that he worries about what treatments might be available to her if the government were given the authority to say what is in her best interest.

"As a father of a little girl, who, if you look up the medical definition of her condition says its incompatible with life, I hesitate to think what those in government and in charge would think, ... how our daughter should be treated and what medical treatments should be available to her if her diagnosis is incompatible with life," Santorum argued.

Patriot Voices, an advocacy organization started by Santorum, has started a petition asking senators to oppose the treaty.

In a Monday press conference, Santorum was joined by Sen. Mike Lee (R-Utah) and Michael Farris, chairman of the Home School Legal Defense Association.

HSLDA worries that the rights of parents who homeschool their children could be impinged if the treaty were passed.

"If the U.S. Senate were to ratify the CRPD, this would give the United Nations the power to influence and change domestic law and threaten parental rights and homeschool freedom," HSLDA Director of Federal Relations William Estrada wrote in a Nov. 19 email to supporters.

Lee, who is leading the effort against the CRPD in the Senate, sent a Sept. 20 letter, signed by himself and 35 other senators, to Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.). The letter does not specifically mention the CRPD, but asks that no treaty be taken up during the lame-duck session (after the election and before the newly elected Senate is seated).

Perhaps ironically, the letter was sent before the election and when many assumed Republicans would gain seats in the election. Republicans actually lost two net seats. So, if the Senate had waited until the new Senate were seated, the CRPD would have a better chance of passage.

Treaties require a two-thirds vote for passage, so if all 36 of the letter's signers vote no, it will fail.

Liberal Washington Post columnist Dana Milbank claimed that the treaty does not undermine parental authority and accused the critics of opposing the disabled and propagating conspiracy theories.

"Their concerns, rather, came from the dark world of U.N. conspiracy theories. The opponents argue that the treaty, like most everything the United Nations does, undermines American sovereignty – in this case via a plot to keep Americans from home-schooling their children and making other decisions about their well-being.